Malignant melanoma in the stomach treated with endoscopic submucosal dissection: a case report

Introduction and Importance: The initial appearance of malignant melanoma localized in the stomach has never been reported previously. We encountered a patient with gastric melanoma in the stomach, which was histologically confirmed to be confined to the mucosa. Case Presentation: The patient, when in her 40s, had undergone surgery for malignant melanoma of the left heel. However, there were no detailed records of pathological findings. The patient had a 4-mm black elevated lesion in her stomach observed on esophagogastroduodenoscopy after the eradication of Helicobacter pylori. A year later, esophagogastroduodenoscopy showed that the lesion had increased to 8 mm. A biopsy was performed, but no malignancy was found; the patient continued to be followed up. Esophagogastroduodenoscopy performed at the 2-year follow-up revealed that the melanotic lesion had increased to 15 mm, and biopsy was performed and revealed a malignant melanoma. Clinical Discussion: Endoscopic submucosal dissection was performed for gastric malignant melanoma. The margin of the resected malignant melanoma was negative; vascular and lymphatic invasions were not observed, and the lesion was confined to the mucosa. Conclusion: We suggest that even if the first biopsy of a melanotic lesion shows no evidence of malignancy, the lesion should be closely monitored. This is the first reported case of endoscopic submucosal dissection of localized gastric malignant melanoma confined to the mucosa.


Introduction
The initial appearance of malignant melanoma in the stomach has never been previously reported. Malignant melanoma has been found to metastasize to all organs, and is the most common carcinoma metastasizing to the gastrointestinal tract [1] . The median survival of patients with gastrointestinal metastases of malignant melanoma has been reported to be 1 year [2] . Herein, we describe a case of gastric malignant melanoma that was endoscopically followed up for 2 years without any particular symptoms, and was managed successfully with endoscopic submucosal dissection (ESD) after another 1 year. The case has been reported in line with the Surgical CAse REport (SCARE) checklist [3] .

Presentation of case
A woman in her 60s presented to the hospital with a complaint of heartburn after being treated for Helicobacter pylori eradication. When in her 40s, she had undergone surgery for malignant melanoma of the left heel. After the malignant melanoma was treated, computed tomography (CT) scans were performed at intervals of 6 months to 1 year for 5 years to monitor the possible appearance of new lesions. However, there were no detailed records of pathological findings. Esophagogastroduodenoscopy showed a black, elevated lesion with a well-defined border of ∼4 mm on the anterior wall of the stomach fundus ( Fig. 1A; 2 years before ESD).
One year later, esophagogastroduodenoscopy showed that the initial lesion had increased to ∼8 mm with a slightly indistinct border ( Fig. 1B; 1 year before ESD). A biopsy was performed; however, no diagnosis of malignant melanoma was made, and the HIGHLIGHTS • Development of malignant melanoma in the stomach was observed for 2 years. • The article reports the first case of endoscopic submucosal dissection of gastric malignant melanoma. • Lesions should be closely monitored even if the initial biopsy shows no melanoma. patient was kept under observation. One year later, esophagogastroduodenoscopy revealed that the lesion had enlarged to 15 mm in size ( Fig. 1C; the year of ESD). Biopsy revealed malignant melanoma confined to the mucosa; however, laboratory tests showed no abnormalities. CT scan from the chest to the pelvic region did not show tumors, thickening of the gastric wall, or lymph node metastasis, but detected a pulmonary nodule of ∼3 mm in diameter (Fig. 1D). Colonoscopy and brain magnetic resonance imaging showed no abnormality, and positron emission tomography-computed tomography presented no accumulation in the pulmonary nodules detected on CT ( Fig. 2A). We consulted a respiratory surgeon about the pulmonary nodule; however, it was difficult to determine whether the lesion was a metastatic tumor because it was only 3 mm in diameter, and the nodule was too small to be resected or biopsied. However, in contrast to the gastric lesions, the nodular lesions in the lung did not expand over the course of the disease. In this case, we used both indigo spraying and narrowband imaging to determine the extent of the malignant melanoma, and it was consistent with the black area noted by ordinary observation. We performed an ESD to remove the malignant melanoma in the stomach (Fig. 2B). We made a mark very close to the tumor, carefully performed precutting around the marking, and successfully obtained a tumor margin of 5 mm. The distribution of the malignant melanoma was consistent with the black elevated lesions of the ESD specimens. The tumor was confined to the epithelium without vascular and lymphatic invasion ( Fig. 2C). Hematoxylin and eosin-stained sections showed tumor cells with vacuolar degeneration and nuclear enlargement (Fig. 2D). On immunohistological analysis, the lesion tested positive for c-kit (Fig. 3A), Melan A (Fig. 3B), HMB-45 (Fig. 3C), and S-100 (Fig. 3D). The margin of the resected tissue was negative both horizontally and vertically. Therefore, it was diagnosed as a malignant melanoma localized in the mucosa. Esophagogastroduodenoscopy was performed 2 months, 8 months, and 1 year after the ESD for course observation. The study was approved by an appropriate ethics committee. Written informed consent was obtained from the patient to publish this case report and any accompanying images.

Discussion
This is the first reported case of ESD of gastric malignant melanoma confined to the mucosa. A keyword search on PubMed for gastric malignant melanoma and ESD revealed no references. Malignant melanoma of the gastrointestinal tract is known to often metastasize from primary skin tumors: 50% to the small intestine, 30% to the colon, and 20% to the rectum. Metastasis in the stomach is rare [4] . Nevertheless, at least 44 cases of primary malignant melanoma have been reported in the past [5] .
Crowley et al. [6] have reported that among 651 patients who were recurrence-free for 10 years after surgery for primary cutaneous malignant melanoma, 168 (25.8%) experienced subsequent recurrence. In this case, the patient developed a gastric lesion 20 years after the surgical removal of cutaneous melanoma. Even though the possibility of it being a primary melanoma of the stomach cannot be excluded, it is more likely to be a secondary delayed recurrence. Previous reports have stated that gastrointestinal malignant melanomas can be classified as either submucosal tumor-like or primary carcinomatous tumors [7,8] . In the present case, the lesion appeared to be a delayed recurrence, but the morphology of the lesion was that of a primary carcinomatous tumor, and it presented as a mildly elevated 0-IIa lesion according to the Japanese classification of gastric carcinoma [9] . Regarding endoscopic resection for gastric malignant melanoma, a case of endoscopic full-thickness resection for gastric metastatic malignant melanoma has been reported previously [10] . However, this is the first case of ESD for malignant melanoma. In our case, biopsy images showed that the melanoma was confined to the mucosa, and the CT scan showed no evidence of gastric wall thickening or lymph node metastasis. The hospital ethics committee discussed the case and recommended ESD for the malignant melanoma according to the usual procedure for early gastric cancer. Pathological findings showed that the malignant melanoma was confined to the mucosa, with negative margins, and negative for vascular and lymphatic invasion; therefore, the resection was locally curative, which does not eradicate the possibility of future recurrence. The patient's postoperative course after the ESD was stable, and esophagogastroduodenoscopy at 2 months, 8 months, and 1-year follow-up showed no recurrence. Although ESD may be considered a treatment option for malignant melanoma less than 20 mm in size, the postoperative follow-up should be for a longer period. However, no conclusion will be provided until evidence accumulates on similar cases.
Furthermore, in the present case, a c-kit examination was performed to investigate the possibility of metastasis from the left heel; the c-kit was positive in this case. C-kit-positive cases have been reported to be more common in mucosal and acral types, including the left heel [11] . Since this is the first case report of submucosal dissection for malignant melanoma, the positivity of the c-kit cannot be discussed further. The significance of c-kit positivity may become clear as similar cases accumulate in the future.
In this case, we were able to follow the course of malignant melanoma of the stomach for 2 years. Although it was considered a complete resection histologically, whether ESD is effective for malignant melanoma remains unclear. The lung nodules and abdomen will be carefully monitored, and in case of any enlargement of the nodules or the appearance of new lesions, treatment will be indicated. In this patient, a 2-year follow-up enabled us to diagnose malignant melanoma.
Therefore, if a black nodule is observed and biopsy does not indicate malignancy, follow-up is required. In the present case, the melanoma was successfully treated after 2 years of follow-up endoscopy; however, we advise that strict follow-up should be performed if similar cases are encountered in the future.

Conclusion
In conclusion, we report the first case of ESD for gastric malignant melanoma. The resection was locally curative. Black elevated lesions should be followed up strictly by endoscopy, even if the first biopsy shows no malignant findings.

Ethical approval
The study was approved by the Ethics Committee of the International University of Health and Welfare Hospital (approval number: 22-B-3).

Patient consent
Written informed consent was obtained from the patient to publish this case report and any accompanying images.

Conflicts of interest disclosure
The authors declare that they have no financial conflict of interest with regard to the content of this report.

Provenance and peer review
Not commissioned, externally peer-reviewed.